1. Technical Field
Aspects of the example embodiments are directed to document capture, and more specifically, smart document capture by estimating scanned-image quality before scanning.
2. Description of Related Art
People are increasingly using cameras of mobile devices (such as cellular phones and personal digital music players) to attempt to scan physical documents. In these situations, the user captures an image of the physical document the usual way: the user must look at the screen of the mobile device. However, camera quality, uneven lighting conditions, and other contextual issues may result in the quality of document images captured with mobile devices being much lower than expected.
Thus, using a mobile device to capture a high quality image of a physical document can be difficult. For example, even if the user is careful to position the physical document in a preview screen of the mobile device, the quality of the final image may not appear as expected based on the preview screen. Furthermore, the act of capturing an image of the physical document may affect the quality of the image, as explained below.
There are a number of potential causes of lost image quality, which may include:
Focus                With a small preview screen, it may not be readily apparent when the focus is slightly off of optimal. Further, even if the mobile device has an autofocus function, autofocus may not be consistent or reliable, especially at the close distances between a mobile device and a physical document, when capturing images of a physical document page. Further, even when correctly focused, the autofocus may refocus before an image can be captured. FIG. 14 provides an example of a blurry captured image which may be captured even if a mobile device is equipped with an autofocus function for the various reasons discussed above.        
Rotation                The frame of the mobile device image may be rotated relative to the page, resulting in a lower resolution of the captured image.        
Framing                When the image is captured, part of the desired content may be cropped, or too much extraneous content may be included. Thus, the resolution of the desired content is reduced due to the difficulty of simultaneously ensuring that multiple edges are correctly framed. FIG. 15 provides an example image of a captured image that is not properly framed and that is rotated relative to the page due to the difficulty of simultaneously ensuring that multiple edges are correctly framed.        
Shadows and Poor Lighting                Poor lighting may result in lower image quality. The act of taking the picture may lower the quality of the image, especially if the user leans over the physical document to see the preview screen, thereby casting a shadow on the document. Further, the shadow may not be apparent when looking at the physical documents, but may be exaggerated in the captured image of the document.        
Depth Variation                The image may not be captured with the plane of the mobile device held parallel to the plane of the physical document. Thus, some parts of the captured image of the document may be more in focus than other parts of the captured image of the document. For example, if the user holds the camera to one side, as someone sitting might do when capturing an image of a page of a physical document on their desk, the camera may not be able to bring into focus the different depths at close range.        
Some of these issues may be handled using post-processing techniques (i.e. image sharpening techniques, image rotating techniques, image cropping techniques, etc.). However, image information may not be fully captured due to above noted issues and not be recoverable by post-processing or post processing may introduce artifacts. Thus, post-processing techniques cannot fully compensate for the above noted issues.
Thus, low camera quality, uneven lighting conditions, and other contextual issues may affect the quality of a captured image with respect to a preliminary image displayed on the screen of the mobile device, even though the cameras on such mobile devices have increasingly higher resolutions. Thus, existing techniques and apparatuses may not be able to provide accurate scans due to poor quality of captured images.